Escalating health care costs have focused national attention on strategies for cost control. This has led some to question whether disproportionate amounts of resources are devoted to the care of the seriously ill and whether access should be limited by criteria of age or prognosis. This public policy debate should be informed by an understanding of the determinants of resource use in the seriously ill and the impact of interventions to enhance patient involvement in decision making. We propose to link the Medicare claims files of 6,581 Medicare beneficiaries with two richly descriptive databases which have examined both the process of decision making and the outcomes of illnesses in seriously ill hospitalized patients in SUPPORT (the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatment) and in hospitalized patients over age 80 (Hospitalized Elderly Longitudinal Project). Unlike previous data collection efforts, these two data bases have information on patient preferences for approach to care, resuscitation, perceived prognosis, and quality of life, based on interviews with patients, their surrogates, and attending physicians during a period of serious illnesses. In the interventional phase of SUPPORT, a multifaceted intervention has been employed to enhance decision making for l ,526 of these patients. Linkage of Medicare claims files with these existing data bases will enable us to perform the following four analyses aimed at informing the public policy discussion. First, the correlates of resource utilization, as represented by adjusted charges and by actual reimbursement, will be examined in the cohort of seriously ill patients and elderly hospitalized patients. Second, we will examine the impact on resource use of two actual interventions aimed at improving decision making: (a) the SUPPORT intervention to improve decision making (on resource use in the ensuing year) and (b) the implementation of the Patient Self-Determination Act, which requires notice about patients' rights to be involved in decision making and to formulate written directives (upon resource use in the last six months of life).